The toxicity of the insect toxin from the venom of the scorpion Androctonus australis Hector has been studied in six species of insects, three species of crustaceans (two terrestrial and one aquatic) and in mice. Paralysing and lethal effects were observed not only in insects but also on the three crustacean species. For insects the LD50 varies from 2 to 1310 ng per 100 mg of insect, according to the species. On crustaceans doses up to 3-9 micrograms per 100 mg of animal induced a paralysing or lethal effect. In mice injections of 0.05 and 1 mg of the toxin intracerebroventricularly and s.c. resulted in no apparent symptoms of intoxication. These results demonstrate that the insect toxin of Androctonus australis Hector has no toxicity for the mouse, but also that it is not absolutely specific for insects.